The primary objective of this study is to determine if the short-term intravenous administration of OTZ (procysteine) results in a clinically relevant decrease in the urinary excretion of oxalate. If this objective is met, it will warrant further testing of oral doses of procysteine in the treatment of primary hyperoxaluria. Two subjects wil be enrolled and will be studied either at the Mayo GCRC or at the Bowman Gray School of Medicine GCRC (Winston-Salem, North Carolina). The subjects enrolled will receive OTZ in a nonblinded fashion with measurements of urine oxalate as well as plasma oxalate, OTZ, and cysteine before and after administration of the drug. If the subjects demonstrate a reduction in urine oxalate excretion of greater than 50 mg/24 hours or >35 mg/gm creatinine of baseline, which would be considered clinically significant in the treatment of this disorder, a separate protocol will be submitted for the study of OTZ or placebo in a blinded, randomized, crossover clinical trial. Duration of the study will be 12 days in the GCRC. This may be completed as a single 12 day stay or two 6 day stays. Constancy of dietary oxalate, calcium, and protein will be maintained throughout the study. OTZ has been studied in animals and humans with human studies thus far conducted in healthy volunteers as well as patients with ARDS, sepsis, and HIV infection. The largest study to date was conducted in over 140 patients with HIV infection. Patients received up to 9000 mg/day of procysteine for a six month period and, in general, the drug was well tolerated and had a favorable safety profile.